Bcdd

[travlnman]

Once again, '78 Z , stock , except for CAI. I made the mistake of removing and cleaning my throttle body on Saturday. Actually that was ok, but I removed the BCDD and cleaned it as well. Must have been stuck, because now I have a high idle at anything above 10mph. It can go as high as 2k, but when I get below 10mph, it comes down. I searched the forum, and lots of people recommend just removing it completely. I'm all for it, but have not found any info on the do's and don'ts of this process. What needs to be blocked off, etc. When I block off the airflow from the air regulator valve, it does not help. I even downloaded the "EFI bible" from a link on the search results, it's good info, but not very specific. If you have done this, I could use the advice. Info is great , pics are awesome, thanks .

[BRAAP]

The BCDD in its simplest description, is a port that bypasses the butterfly in the Throttle body and have valve in that port that allows air to by pass the closed Butterfly under certain conditions.

 

In removing the BCDD for the throttle body, you will see two large ports in the throttle body itself, (GREEN in the picture below). Both of those need to be plugged. I prefer to tap them and use a large short bolt or pipe plug, then cover that in JB weld for a good seal. Do NOT use just JB weld only to fill the holes! The JB weld could come loose and get sucked into the engine, NOT good!

The 2 smaller ports also need to be plugged, (MAGENTA in the picture below). Again, small screws and sealed. Or, after the large ports are plugged, a metal plate with gasket that covers the entire bottom of the Throttle body will seal off those two smaller ports.

 

Another option is to use the later ZX Throttle body, though be aware the later ZX Throttle body is thinner where the boot attaches, as such, the S30 boot doesn’t fit real well! (The ID of ALL L28 Throttle bodies, Turbo, N/A early, late, etc are the same, the OD where the boot attaches is smaller, thinner wall, for the later NON BCDD Throttle bodies!)

 

Hope this helps.

 

[travlnman]

That , sir, was awesome ! That will be my first priority, at least when I get home from Chicago this week. Maybe that will teach me to leave well enough alone. BTW, what's the deal with the 10 mph ? I thought I remembered reading that it was tied to the speedo somehow, but I read through so many threads and posts, it's all a little foggy now. Thanks again, this forum by far has the best activity and knowledge that I have found so far !

[BRAAP]

That , sir, was awesome ! That will be my first priority, at least when I get home from Chicago this week. Maybe that will teach me to leave well enough alone. BTW, what's the deal with the 10 mph ? I thought I remembered reading that it was tied to the speedo somehow, but I read through so many threads and posts, it's all a little foggy now. Thanks again, this forum by far has the best activity and knowledge that I have found so far !

 

I don't recall how where the speed thing is tied in, probably wouldn't retain that info any how.

 

Glad that helped.

 

Take care,

Paul

[travlnman]

I understand. I searched BCDD, and a LOT of stuff came up. I read posts til my eyes blurred. I remember reading that, but I can't be sure that it was definitely tied to the BCDD, or air regulator or something else entirely. Keep up the good work !